The Department of Energy is currently developing in-situ barrier emplacement techniques and materials for the containment of high-risk contaminants in soils. Injected grouts, waxes, polymers, slurries and freezing of soil moisture are barrier techniques currently under development and/or being demonstrated. Because of their relatively high cost, the barriers are intended to be used in cases where the risk is too great to remove the contaminants, the contaminants are too difficult to remove with current technologies, or the potential movement of the contaminants to the water table is so high that immediate action needs to be taken to reduce health risks. Consequently, barriers are primarily intended for use in high-risk sites where few viable alternatives exist to stop the movement of contaminants in the near term. The intent of these designs is to prevent the movement of contaminants in either the liquid or vapor essentially buying time until remediation can be implemented or until the contaminant depletes naturally. Assessing the integrity of the barrier once it is emplaced, and during its anticipated life, is a very difficult but necessary requirement.
Surface based geophysical techniques, such as ground penetrating radar, electromagnetic, or seismic surveys, can only detect the presence of barrier materials in the soil. They are incapable of resolving imperfections on the scale of fractions of an inch, which is required to assess the integrity of these subsurface structures. Borehole geophysical techniques (neutron, gamma, EM and acoustic tomograph) are potentially capable of the required resolution, but because of the measurement depth (fractions of meters) necessary to attain the desired resolution, many closely spaced access holes are needed to perform the integrity validation function. Because of the limitations in geophysical techniques (and limited hope that their resolution can be practically improved) gaseous tracers have been suggested. See "Subsurface Barrier Verification Technologies," J. H. Jeiser, BNL-61127, Brookhaven National Laboratory, June 1994.
Tracers have been used previously for landfill liner and underground storage tank leak detection. A typical usage is to inject small amounts of perfluorocarbon tracer gas and monitor for its appearance on the other side of an impermeable layer (such as landfill liner or UST wall). Several different tracers can be used to distinguish leak locations. Gas analysis is usually done with GC-MS or similar sophisticated analytic device, and inference of leakage characteristics accomplished by post test analysis of the soil gas data. This is a time consuming, artful process. The challenge with the use of tracers is to develop a system which automatically assesses barrier integrity in real time, to avoid time consuming and expensive numerical back-calculations.
The present invention is a turn-key, autonomous monitoring system to provide leakage characteristics in real time. This will significantly reduce the labor required for assessment of barrier integrity. The conservative vapor testing methodology, combined with the real time assessment, introduces the possibility that breaches in a barrier can be repaired before liquid contaminant is released from the contained volume.
The present invention has the following benefits:
Reducing public and occupational health risks by assuring that the integrity of barriers intended to contain high risk contaminants. As such, it will quantify leaks so that remedial actions (repairs) can be accomplished to minimize risk to the public. The method of sampling system installation (direct push or ResonantSonic.TM.) minimizes occupational risk by reduction of secondary waste generation. PA1 Improving cleanup operations by assuming that barriers are constructed as desired. PA1 Cost reduction. PA1 Ability to meet regulatory requriements. PA1 It measures vapor leaks in a containment system whose greatest risk is posed by liquid leaks; PA1 It is applicable to any impermeable barrier emplacement technology in the unsaturated zone; PA1 It qualifies both the leak location and size; PA1 It uses readily available, non-toxic, inexpensive, nonhazardous gaseous tracers; PA1 The vapor injection and sampling points can be emplaced by direct push techniques (such as Geoprobes) or the rapid ResonantSonic.TM. technique, avoiding excessive drilling costs and secondary waste generation; PA1 It provides continuous and unattended contaminant plume measurements for remote site operation; PA1 In incorporates the methodology for unfolding the soil gas analysis data in real time using a rigorous inverse modeling technique which accommodates uncertainties in field data; and PA1 In addition to assessing initial barrier integrity, the system can also provide long term monitoring of contaminant soil gases for surveillance of the containment system's performance over time.
The present invention is applicable to the assessment of any impermeable barrier constructed above the water table. Furthermore, the system is equally capable of performing as the long term monitoring system of the barrier's integrity.